Blow-flies (also frequently spelled blow flies or blowflies), carrion-flies or bottle flies are members of the family Calliphoridae of flies (Diptera). Some members of this family are known as bluebottles, clusterflies or greenbottles. Flies in this family are often metallic in appearance and between 10 to 12 mm in length.
The name blow-fly comes from an older English term for meat that had eggs laid on it, which was said to be fly blown. The first association of the term “blow” with flies was used by William Shakespeare in his plays Loves Labour Lost, The Tempest, and Antony and Cleopatra.
The characteristics and arrangement of hairs are used to tell the difference between members of this family. All blow-flies have bristles located on the meron. Having two notopleural bristles and a hindmost posthumeral bristle located lateral to pre-sutural bristle are characteristics to look for when identifying this family.
The thorax has the continuous dorsal suture across the middle, along with well defined posterior calli. The post-scutellum is absent or weakly developed. The costa is unbroken and the sub-costa is apparent on the insect.
Most species of blowflies studied thus far are anautogenous; a female requires a substantial amount of protein to develop mature eggs within her ovaries (about 800 µg per pair of ovaries in Phormia regina). The current theory is that females visit carrion both for protein and egg laying, but this remains to be proven. Blow-fly eggs,usually yellowish or white in color, are approximately 1.5 mm x 0.4 mm, and, when laid, look like rice balls. While the female blow-fly typically lays 150-200 eggs per batch, she is usually iteroparous, laying around 2,000 eggs during the course of her life. The sex ratio of blowfly eggs is usually 50:50, but one interesting exception is currently documented in the literature. Females from two species of the genus Chrysomya (C. rufifacies and C. albiceps) are either arrhenogenic (laying only male offspring) or thelygenic (laying only female offspring).
Hatching from an egg to the first larval stage takes about 8 hours to one day. Larvae have three stages of development (called instars); each stage is separated by a molting event.The instars are separable by examining the posterior spiracles, or openings to the breathing system The larvae use proteolytic enzymes in their excreta (as well as mechanical grinding by mouth hooks) to break down proteins on the livestock or corpse they are feeding on. Blowflies are poikilothermic, which is to say that the rate at which they grow and develop is highly dependent on temperature and species. Under room temperature (about 30 degrees Celsius) the black blowfly Phormia regina can go from egg to pupa in 150-266 hours (6 to 11 days). When the third stage is complete the pupa will leave the corpse and burrow into the ground, emerging as an adult 7 to 14 days later.
Adult blow-flies are occasional pollinators, being attracted to flowers with a strong odor resembling rotting meat, such as the American pawpaw or Dead Horse Arum. There is little doubt that these flies utilize nectar as a source of carbohydrates to fuel flight, but just how and when this happens is unknown. One study has been done to prove that the visual stimulus a blow-fly receives from its compound eyes is what is responsible for causing its legs to retract from their flight position and allow it to land on any surface.
Larvae of most species are scavengers of carrion and dung and most likely constitute the majority of the maggots found in such material, although it is not uncommon for them to be found in close associate with other dipterous larvae from the families Sarcophagidae, Muscidae, and many other acalyptrate muscoid flies.
The typical habitat for blow-flies are temperate to tropical areas that provide a layer of loose, damp soil and litter where larvae may thrive and pupate.
Sources: MYIA, FE, Nomina, A/O DC
The most common causes of myiasis in humans and animals are the three dipteran families Oestridea, Calliphoridae, and Sarcophagidae. Myiasis in humans is clinically categorized in six ways: dermal and subdermal, facial cavity, wound or traumatic, gastrointestinal, vaginal, and generalized myiasis. If found in humans, the diptera larvae are usually in their first instar. The only treatment necessary is just to remove the maggots, and the patient heals naturally.
The secondary screwworm (Cochliomyia macellaria) has become one of the principal species on which to base postmortem interval estimations because its succession and occurrence on decomposing remains has been well defined. The secondary screwworm is found throughout the United States, the American tropics, and in southern Canada during summer months. This species is one of the most common species found on decomposing remains in the southern United States.
Paratuberculosis in cattle, pigs and birds (M. a. avium) have been isolated and recovered from these flies through several different experiments.
Other potential vectors and threatening diseases include Rabbit Hemorrhagic Disease Virus in New Zealand and Strike. Although Strike is not limited to blow flies; these maggots are a major source of this skin invasion causing lesions, and if severe enough, may be lethal. Strike starts when blow-flies lay eggs in a wound or fecal material present on the sheep. When the maggots hatch, they begin feeding on the sheep and thus irritating it. As soon as the first wave of maggots hatch, they attract more blow-flies causing the Strike. Currently, there is no insecticides for blowfly prevention, but precautionary measures may be taken, such as docking tails, shearing, and keeping the sheep overall healthy.
Salmonellosis has also been proven to be transmitted by the blow fly through saliva, feces and tarsi. Adult flies may be able to spread pathogens via their sponging mouthparts, vomit, intestinal tract, sticky pads of their feet or even their body or leg hairs.
As vectors of many diseases, the importance of identifying the transmissible agents, the route and prevention are becoming increasingly important. With the ability to lay hundreds of eggs in a lifetime and the presence of thousands of larvae at a time in such close proximity, the potential for transmission is high especially at ideal temperatures.
Blow-flies are usually the first insects to come in contact with carrion because they have the ability to smell death from up to ten miles (16 km) away. Upon reaching the carrion, females deposit eggs onto the body. Since development is highly predictable if the ambient temperature is known, blow-flies are considered a valuable tool in forensic science. Traditional estimations of time since death (namely rigor mortis and algor mortis) are generally unreliable after 72 hours and often entomologists are the only officials capable of generating an accurate approximate time interval. The specialized discipline related to this practice is known as forensic entomology
Calliphora vicina and Cynomya mortuorum are important flies of forensic entomology. Other forensically important Calliphoridae are Phormia regina, Calliphora vomitoria, Calliphora livida, Lucilia cuprina, Lucilia sericata, Lucilia illustris, Chrysomya rufifacies, Chrysomya megacephala, and Cochliomyia macellaria. One interesting myth states that species from the genus Lucilia can sense death and show up right before it even occurs.